Printed material discloses a great number of proposals for cleaning contaminated soil; cf., for example, the article "CLEANING EXCAVATED SOIL USING EXTRACTION AGENTS: A STATE-OF-THE-ART REVIEW" BY R. Raghavan et al., U.S. Environmental Protection Agency EPA/600/2-89/034 of June 1989, and more specifically the literature references given in the pages 46-50 therein.
A number of operations have been designed for the use on an industrial large scale and may be exemplified by excerpts from the following:
______________________________________ Primary Unit Operations Reference ______________________________________ Extraction, flotation Nunno, Hyman and Pheiffer (1988); Assink (1987) Extraction, hydrocyclones Nunno, Hyman and Pheiffer (1988): Assink (1987) Floatation Nunno, Hyman and low frequency vibration (1988); Sonnen and Klingebiel (1988) Water-jet scrubber Heimhard (1988) Solvent extraction Nunno, Hyman and Pheiffer (1988) Water-Knife Scrubber, Traver and Freestone Extraction (1985) Scholz and Milanowski (1983) Trommel washer, Ayres (1990) jig separator ______________________________________
U.S. Pat. No. 4,784,757, issued on Nov. 15, 1988, to Nelson and McClung, relates to a device for the separation of solids of different specific gravities by means of a substantially laminar upward flow of water, especially for facilitating the recovery of gold from mineral feedstock. The device presented in said U.S. patent specification in particular is distinguished in that the material separation of the mineral feedstock mixtures listed can be achieved at a minimum expenditure of those working elements required to be kept in motion. U.S. Pat. No. 4,784,757 provides for the use of water as separation and transferring liquid, wherein an ascending stream of the water employed as the separation liquid, the larger and/or heavier particles will settle and be discharged from the bottom of the separation zone, while smaller and/or lighter solid particles are carried upward and discharged from the top of the separation zone. It was stated that the effluent in an amount of about 90% of the initial water stream is free from finely divided particulate contaminants and may be returned to the source it was taken from.
The present invention is based on the recognition that the separation procedure outline in said U.S. patent makes a suitable starting point for the development of a highly efficient process in order to attain the objects of this invention. The teaching provided hereinbelow of the invention describes the further developments and the device members and process features by means of which the mixing, cleaning, separation and/or preconditioning of the feedstock can be accomplished, said device members and process features having been clearly improved in various ways over cited references.
Prior attempts at material separation devices and processes have been plagued with a number of different problems, namely: they use and discharge too much separation fluid or water; they have been unable to separate fine and finely differentiated particles with any reasonable degree of efficiency or effectiveness; they have been unable to provide such a process or device which is relatively inexpensive to construct and operate; and they have been unable to provide a system that operates effectively despite wide variations in the composition of the feedstock.
This invention solves the forenamed problems to a degree not heretofore achieved on any scale, let alone for a commercial production unit capable of continuous production.